1. Field of the Invention
The present invention relates to battery packs in which a plurality of unit cells is arranged to be connected together and stored in a housing.
2. Description of the Related Art
A patent document 1, Japanese patent laid open publication No. 2004-311157, has disclosed a conventional battery pack having a cooling structure capable of introducing outside air into the inside of the battery pack to cool a plurality of unit cells. In order to effectively perform a temperature control of each of the unit cells, the unit cells are arranged at regular intervals. The introduced outside air is used as cooling air and supplied between the unit cells arranged at regular intervals, and the cooling air containing heat energy is then discharged to the outside of the battery pack.
However in the structure of the conventional battery pack according to the patent document 1 as previously described, it is difficult to completely radiate heat energy of the unit cells by cooling air at one time, so that a large temperature difference occurs between the unit cells and the cooling air passed through the unit cells 11. In order to further decrease the temperature of the unit cells in the battery pack, it is necessary to use a fan to supply additional cooling air. However, noise such as fan noise is generated and the magnitude of fan noise is increased when a rotary speed of the fan becomes high in order to further increase the cooling capability for the unit cells. Still further, a temperature of each of the unit cells varies between the upstream side and the downstream side thereof even if the unit cells are arranged at regular intervals.